[Sirtel]

You can create as many separate libraries with Calibre as you like, and switch between them with a couple of clicks, even when your device is connected.

Click on the library icon and choose switch/create library. If you already have an existing library, choose Use the previously existing library at the new location and select the folder your library is in. If you want to create an entirely new library, choose Create an empty library at the new location and select the folder you want your new library to be in.

Once the libraries are created, you can switch between them by clicking on the library icon and choosing the library name from the dropdown. You can switch before you connect the Kindle or when the Kindle is already connected, there's no difference.